NAME

enc2xs -- Perl Encode Module Generator

SYNOPSIS

enc2xs -[options]
enc2xs -M ModName mapfiles...
enc2xs -C

DESCRIPTION

enc2xs builds a Perl extension for use by Encode from either
Unicode Character Mapping files (.ucm) or Tcl Encoding Files
(.enc). Besides being used internally during the build pro-
cess of the Encode module, you can use enc2xs to add your
own encoding to perl. No knowledge of XS is necessary.

Quick Guide

If you want to know as little about Perl as possible but
need to add a new encoding, just read this chapter and for-
get the rest.
0. Have a .ucm file ready. You can get it from somewhere
or you can write your own from scratch or you can grab
one from the Encode distribution and customize it. For
the UCM format, see the next Chapter. In the example
below, I'll call my theoretical encoding myascii,
defined in my.ucm. "$" is a shell prompt.
$ ls -F
my.ucm
1. Issue a command as follows;
$ enc2xs -M My my.ucm
generating Makefile.PL
generating My.pm
generating README
generating Changes
Now take a look at your current directory. It should
look like this.
$ ls -F
Makefile.PL My.pm my.ucm t/
The following files were created.
Makefile.PL - MakeMaker script
My.pm - Encode submodule
t/My.t - test file
1.1.
If you want *.ucm installed together with the
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modules, do as follows;
$ mkdir Encode
$ mv *.ucm Encode
$ enc2xs -M My Encode/*ucm
2. Edit the files generated. You don't have to if you have
no time AND no intention to give it to someone else.
But it is a good idea to edit the pod and to add more
tests.
3. Now issue a command all Perl Mongers love:
$ perl Makefile.PL
Writing Makefile for Encode::My
4. Now all you have to do is make.
$ make
cp My.pm blib/lib/Encode/My.pm
/usr/local/bin/perl /usr/local/bin/enc2xs -Q -O \
-o encode_t.c -f encode_t.fnm
Reading myascii (myascii)
Writing compiled form
128 bytes in string tables
384 bytes (75%) saved spotting duplicates
1 bytes (0.775%) saved using substrings
....
chmod 644 blib/arch/auto/Encode/My/My.bs
$
The time it takes varies depending on how fast your
machine is and how large your encoding is. Unless you
are working on something big like euc-tw, it won't take
too long.
5. You can "make install" already but you should test
first.
$ make test
PERL_DL_NONLAZY=1 /usr/local/bin/perl -Iblib/arch -Iblib/lib \
-e 'use Test::Harness qw(&runtests $verbose); \
$verbose=0; runtests @ARGV;' t/*.t
t/My....ok
All tests successful.
Files=1, Tests=2, 0 wallclock secs
( 0.09 cusr + 0.01 csys = 0.09 CPU)
6. If you are content with the test result, just "make
install"
7. If you want to add your encoding to Encode's demand-
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loading list (so you don't have to "use
Encode::YourEncoding"), run
enc2xs -C
to update Encode::ConfigLocal, a module that controls
local settings. After that, "use Encode;" is enough to
load your encodings on demand.

The Unicode Character Map

Encode uses the Unicode Character Map (UCM) format for
source character mappings. This format is used by IBM's ICU
package and was adopted by Nick Ing-Simmons for use with the
Encode module. Since UCM is more flexible than Tcl's Encod-
ing Map and far more user-friendly, this is the recommended
formet for Encode now.
A UCM file looks like this.
#
# Comments
#
<code_set_name> "US-ascii" # Required
<code_set_alias> "ascii" # Optional
<mb_cur_min> 1 # Required; usually 1
<mb_cur_max> 1 # Max. # of bytes/char
<subchar> \x3F # Substitution char
#
CHARMAP
<U0000> \x00 |0 # <control>
<U0001> \x01 |0 # <control>
<U0002> \x02 |0 # <control>
....
<U007C> \x7C |0 # VERTICAL LINE
<U007D> \x7D |0 # RIGHT CURLY BRACKET
<U007E> \x7E |0 # TILDE
<U007F> \x7F |0 # <control>
END CHARMAP
+ Anything that follows "#" is treated as a comment.
+ The header section continues until a line containing the
word CHARMAP. This section has a form of <keyword>
value, one pair per line. Strings used as values must
be quoted. Barewords are treated as numbers. \xXX
represents a byte.
Most of the keywords are self-explanatory. subchar means
substitution character, not subcharacter. When you
decode a Unicode sequence to this encoding but no match-
ing character is found, the byte sequence defined here
will be used. For most cases, the value here is \x3F;
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in ASCII, this is a question mark.
+ CHARMAP starts the character map section. Each line has
a form as follows:
<UXXXX> \xXX.. |0 # comment
^ ^ ^
| | +- Fallback flag
| +-------- Encoded byte sequence
+-------------- Unicode Character ID in hex
The format is roughly the same as a header section
except for the fallback flag: | followed by 0..3. The
meaning of the possible values is as follows:
|0 Round trip safe. A character decoded to Unicode
encodes back to the same byte sequence. Most char-
acters have this flag.
|1 Fallback for unicode -> encoding. When seen, enc2xs
adds this character for the encode map only.
|2 Skip sub-char mapping should there be no code point.
|3 Fallback for encoding -> unicode. When seen, enc2xs
adds this character for the decode map only.
+ And finally, END OF CHARMAP ends the section.
When you are manually creating a UCM file, you should copy
ascii.ucm or an existing encoding which is close to yours,
rather than write your own from scratch.
When you do so, make sure you leave at least U0000 to U0020
as is, unless your environment is EBCDIC.
CAVEAT: not all features in UCM are implemented. For exam-
ple, icu:state is not used. Because of that, you need to
write a perl module if you want to support algorithmical
encodings, notably the ISO-2022 series. Such modules
include Encode::JP::2022_JP, Encode::KR::2022_KR, and
Encode::TW::HZ.
Coping with duplicate mappings
When you create a map, you SHOULD make your mappings round-
trip safe. That is, "encode('your-encoding',
decode('your-encoding', $data)) eq $data" stands for all
characters that are marked as "|0". Here is how to make
sure:
+ Sort your map in Unicode order.
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+ When you have a duplicate entry, mark either one with
'|1' or '|3'.
+ And make sure the '|1' or '|3' entry FOLLOWS the '|0'
entry.
Here is an example from big5-eten.
<U2550> \xF9\xF9 |0
<U2550> \xA2\xA4 |3
Internally Encoding -> Unicode and Unicode -> Encoding Map
looks like this;
E to U U to E
--------------------------------------
\xF9\xF9 => U2550 U2550 => \xF9\xF9
\xA2\xA4 => U2550
So it is round-trip safe for \xF9\xF9. But if the line
above is upside down, here is what happens.
E to U U to E
--------------------------------------
\xA2\xA4 => U2550 U2550 => \xF9\xF9
(\xF9\xF9 => U2550 is now overwritten!)
The Encode package comes with ucmlint, a crude but suffi-
cient utility to check the integrity of a UCM file. Check
under the Encode/bin directory for this.
When in doubt, you can use ucmsort, yet another utility
under Encode/bin directory.